Constant output light attenuator and constant output light attenuating method

ABSTRACT

In a light attenuator or its attenuating method, a nonlinear optical material and an aperture section are placed respectively on a same optical axis, between a receiving optical fiber and a sending optical fiber. The nonlinear optical material receives and refracts an input light outputted from the receiving optical fiber. The aperture section has an aperture, receives the light having passed through the nonlinear optical material, and outputs constant output light to the sending optical fiber by only allowing a part of the light to be outputted from the aperture. Then, for obtaining the wishful output light with constant strength no depending upon the input light, these parameters of the quadratic nonlinear refractive index n2 and the thickness t of the nonlinear optical material; the distance L between nonlinear optical material and aperture section; and the diameter Ø of the aperture, are set most appropriately.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present Invention relates to a light attenuator which canapproximately obtain constant outputting light strength and itsattenuating method.

[0003] 2. Description of the Related Art

[0004] In the adjustment of light strength of optical communicationnetwork or optical equipment, light attenuator is applied. Specially,with the development of recent transmitting system of Dense WavelengthDivision Multiplexing (DWDM), the request with respect to the lightattenuator is rapidly increasing. In the concrete, the light attenuatoris used in the field of a light strength adjusting unit or a lightamplifier of the translator in optical communication network. Also, thelight attenuator is used in a light strength adjusting unit of opticalequipment relating to a variety of light sources, for example, a laserdiode (LD) light source or the like. Further, the light attenuator isused in a unit being for protecting a light detector to detect a highstrength light.

[0005] In the light attenuators used for adjusting light strength or thelike, currently, a fixed type and a variable type optical attenuatingunits are known.

[0006] On the one hand, the fixed type optical attenuating unit is usedfor obtaining predetermined attenuating amount by using attenuatingfilter or optical fiber added a attenuating dopant. In response to theattenuating amount, these fixed type optical attenuating units areclassified.

[0007] On the other hand, the variable type optical attenuating unitincludes a mechanical form light attenuator and a non-mechanical formlight attenuator.

[0008] In the variable type optical attenuating units of mechanical,there are a type using a method which transfer light in space andattenuates the light; a type using a method which inserts a moveableattenuating optical filter into a light path; a type which quiversslightly optical fibers whose optical axes are corresponding to eachother so as to cause a deviation between optical axes; and so on.

[0009] Also, in the variable type optical attenuating unit ofnon-mechanical, there are a Faraday effect type; a wave guide path type;a polymer wave guide path type using thermal optics; a Mach-Zehnder(Mach-Zender) wave guide path (waveguide) type; and so on.

[0010] However, in the above prior art, there is a following subject tobe solved.

[0011] For example, In the case that a optical communication networkwork is performed in which light strength in transferring path ischanged, It is necessary to use a light attenuator whose attenuatingamount must conform to the desired that in the transferring path.

[0012] Thus, when using a fixed type optical attenuating unit, becausethe attenuating amount of the fixed type optical attenuating unit isdefinite, to obtaining desired attenuating amount in the transferringpath, the light attenuator is often exchanged with the attenuatingamount in the transferring path changes. Because of this, there is aproblem that, with the light strength changes sharply, It is impossibleto correspond quickly to the change.

[0013] As compared with this, though the variable type opticalattenuating unit has not the above problem like the fixed type opticalattenuating unit, because the current variable type optical attenuatingunit must be controlled electrically, electrical power is consumed.Moreover, when generating heat in using, because a driver is necessaryfor a attenuating amount control, the driver is assembled into a controlunit. Therefore, there is a problem that the unit is large-sized.

SUMMARY OF THE INVENTION

[0014] In view of the above, the present invention is, neither dependupon the inputted light strength nor need the electrical control, tosupplies a light attenuator and a light attenuating method for obtainingconstant outputted light strength.

[0015] The present invention with constant outputted light strengthcomprises:

[0016] a nonlinear optical material whose refractive index changesdepending upon the light strength of input light; and

[0017] an aperture section which receives the light outputted from thenonlinear optical material and allows only, in the received light, thelight within a definite radius from a optical axis to pass through.

[0018] Therefore, in light attenuating method using the light attenuatorof the present invention, it is possible to always obtain constantoutputted light strength no depending upon the light strength of inputlight. The inventions relating to the light attenuator and lightattenuating method can attain the objective by the following-describedmeans.

[0019] (1) According to a first aspect of the present invention, thereis provided a constant output light attenuator, comprising:

[0020] a nonlinear optical material whose refractive index changesdepending upon the light strength of input light; and

[0021] an aperture section which is placed at the optical axis of thenonlinear optical material, receives the light outputted from thenonlinear optical material, and allow only the light within a definiteradius from the optical axis to pass through.

[0022] (2) In the light attenuator of the present invention, thenonlinear optical material may be selected from any one of a corpuscledispersion glass, an optical ceramics and an organic macromoleculematerial.

[0023] (3) Also, the nonlinear optical material may have an incidentsurface and a radiant surface, the incident surface lies at right angleto the optical axis, and the radiant surface inclines toward the opticalaxis with a predetermined angle.

[0024] (4) Also, on the optical axis at incident side of the nonlinearoptical material, a convex lens may be placed.

[0025] (5) Also, at the incident side of the nonlinear optical material,a slit section may be placed whose central part of the major axis isplaced a location deviating from the optical axis.

[0026] (6) Also, at the incident side of the nonlinear optical material,a convex lens and a slit section may be placed. The convex lens isplaced on the optical axis, and the slit section is placed a location bymaking the central part of the major axis to deviate from the opticalaxis.

[0027] (7) Also, the nonlinear optical material may be make up of anoptical fiber whose core has nonlinear optical effect.

[0028] (8) In this case, the core may be make up of a corpuscledispersion glass.

[0029] (9) Further, the core may be make up of a material that has aquadratic nonlinear refractive index depending upon wavelength.

[0030] (10) In this case, the core may be make up of a material whosequadratic nonlinear refractive index is positive.

[0031] (11) Also, the core may be make up of a material whose quadraticnonlinear refractive index is negative.

[0032] (12) According to a second aspect of the present invention, thereis provided a constant output light attenuating method, comprising:

[0033] outputting a light from a nonlinear optical material whoserefractive index changes depending upon the light strength of inputlight, by making the input light pass through the nonlinear opticalmaterial;

[0034] receiving the light outputted from the nonlinear optical materialby using a aperture section which is placed at a optical axis of thenonlinear optical material;

[0035] attenuating the received light by allowing only the light withina definite radius from the optical axis to pass through, by the aperturesection.

[0036] In the light attenuating method of the present invention, thenonlinear optical material may be make up of the one selected from anyone of a corpuscle dispersion glass, an optical ceramics and a organicmacromolecule material.

[0037] (13) Also, the nonlinear optical material may have an incidentsurface and a radiant surface, the incident surface lies at right angleto the optical axis, and the radiant surface inclines toward the opticalaxis with a predetermined angle.

[0038] (14) Also, at the optical axis of incident side of the nonlinearoptical material, a convex lens may be placed. In this case, in thiscase, a light first pass through the convex lens, then serves as inputlight to pass through the nonlinear optical material.

[0039] (15) Also, at the incident side of the nonlinear opticalmaterial, a slit section having a slit may be placed whose central partof the major axis is placed a location deviating from the optical axis.In this case, a light first pass through the slit, then serves as inputlight to pass through the nonlinear optical material

[0040] (16) Also, at the incident side of the nonlinear opticalmaterial, a convex lens and a slit section may be placed.

[0041] (17) The convex lens is placed on the optical axis, and the slitsection is placed a location by making the central part of the majoraxis deviate from the optical axis. In this case, a light first passthrough the convex lens and the slit, then serves as input light to passthrough the nonlinear optical material

[0042] (18) Also, the nonlinear optical material may be make up of anoptical fiber whose core has nonlinear optical effect.

[0043] (19) In this case, the core may be make up of a corpuscledispersion glass.

[0044] (20) Further, the core may be make up of a material that has aquadratic nonlinear refractive index depending upon wavelength.

[0045] (21) In this case, the core may be make up of a material whosequadratic nonlinear refractive index is positive.

[0046] (22) Also, the core may be make up of a material whose quadraticnonlinear refractive index is negative.

BRIEF DESCRIPTION OF THE DRAWINGS

[0047] The above and other objects, advantages and features of thepresent invention will be more apparent from the following descriptiontaken in conjunction with the accompanying drawings in which:

[0048]FIG. 1 is a longitudinal section showing the relation between alight attenuator of the present invention in one embodiment and the endportion of an optical fiber.

[0049]FIG. 2 is an explanation diagram showing the characteristic of alight attenuator of the present invention.

[0050]FIG. 3 is a longitudinal section showing the relation between alight attenuator of the present invention in other embodiment and theend portion of an optical fiber.

[0051]FIG. 4 is a longitudinal section showing the relation between alight attenuator of the present invention in more other embodiment andthe end portion of an optical fiber.

[0052]FIG. 5 is a longitudinal section showing the relation between alight attenuator of the present invention in more other embodiment andthe end portion of an optical fiber.

[0053]FIG. 6 is a longitudinal section showing the relation between alight attenuator of the present invention in more other embodiment andthe end portion of an optical fiber.

[0054]FIG. 7 is a longitudinal section showing the relation between alight attenuator of the present invention in more other embodiment andthe end portion of an optical fiber.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0055] Best modes of carrying out the present invention will bedescribed in further detail using various embodiments with references tothe accompanying drawing.

[0056] Embodiment 1:

[0057]FIG. 1 is a longitudinal section showing the relation between alight attenuator of the present invention in one embodiment and the endportion of an optical fiber.

[0058] The light attenuator of the present invention comprises anonlinear optical material 1 and an aperture section 2 as shown byFIG. 1. The nonlinear optical material 1 and the aperture section 2 areplaced respectively on an optical axis, together with a receivingoptical fiber 3 used to receive a light and a sending optical fiber 4used to send out a light. The light outputted from the receiving opticalfiber 3, as input light, enters and passes through the nonlinear opticalmaterial 1. The light having passed through the nonlinear opticalmaterial 1 is spreading toward the radiant direction apart from theoptical axis as a center. The aperture section 2 has an aperture, andwith respect to the spreading light, the aperture only allows only thelight within a definite radius of the optical axis to pass through. Thelight having passed through the aperture section 2 enters the sendingoptical fiber 4. In this case, by making a variety of parameter statedas follows conform mostly, the output light with constant strength canbe obtained.

[0059] The object of the present invention, as stated above, is tosupply a light attenuator and a light attenuating method that can alwaysobtain approximate constant outputted light strength, rather thandepending upon the strength of a input light. Now by combining thenonlinear optical material 1 and the aperture section 2, the object canbe realized.

[0060] The nonlinear optical material 1 is a matter whose refractiveindex changes depending upon the light strength of input light. Therefractive index is shown by the following expression:

n=n ₀ +n ₂ |E| ²  (1)

[0061] Here in, the n0 is fixed refractive index that does not changedepending upon light strength, n2 is quadratic nonlinear refractiveindex, E is light strength.

[0062] On the one hand, when the light strength of input light is weak,because it is possible to ignore the item “n₂|E|²” stated above, therefractive index of the nonlinear optical material 1 is constantapproximately, as shown by FIG. 1(a). In the FIG. 1(a), the parallellight outputted from the receiving optical fiber 3, is passing throughthe nonlinear optical material 1 and entering the sending optical fiber4 intact. Therefore, in this case, if ignoring the attenuate in thenonlinear optical material 1 of the parallel light, the parallel lightoutputted from the receiving optical fiber 3, enters the sending opticalfiber 4, in almost no-attenuate state.

[0063] On the other hand, when the light strength of input light isstrong, the influence of the item “n₂|E |²” becomes bigger. That is,because the refractive index of the nonlinear optical material 1 changesdepending upon the light strength of input light, the input lightentering the nonlinear optical material 1 is refracted then outputs whenthe input light becomes stronger, as shown by FIG. 1(b). In this case,the nonlinear optical material 1 performs a function of a convex lens.In the FIG. 1(b), the refracted light outputted from the nonlinearoptical material 1 is passing through a focus between the nonlinearoptical material 1 and the aperture section 2, and spreading toward theradiant direction apart from the focus as a starting point.

[0064] However, in the spreading light, the partial light on the outsideis cut off by the aperture section 2. That is, the spreading light isattenuated by the aperture section 2. In other words, the aperturesection 2 limited the spreading light. Thus, only the partial lightwithin a definite radius from the optical axis as a center passesthrough the aperture section 2 and enters the sending optical fiber 4.Therefore, in this case that the light strength of the input light isbigger, Because the light outputted from the receiving optical fiber 3is attenuated automatically by the aperture section 2, the light amountof the light entering the sending optical fiber 4 falls.

[0065] According to the above, the more strong the light strength of theinput light is, the more big the light attenuating amount is. Further,the aperture section 2 stated above, has an aperture. The aperture is acircular opening that has a predetermined radius and is surrounding theoptical axis as a center. When observing along the radius direction, theaperture makes the optical beam having regular thickness to passthrough. Therefore, the partial light outside of the circular opening iscut off.

[0066] Moreover, regarding the nonlinear optical material 1 used in thisembodiment, a corpuscle dispersion glass in which the corpuscle of suchas copper or copper chloride or the like is dispersed; an opticalceramics of PLZT (a crystal formed by an oxide of Plumbum and Lanthan,and an oxide of Zirconium and Titan) or the like; or an organicmacromolecule material of polydiacetylene or the like; etc. can be used.

[0067]FIG. 2 is an explanation diagram showing the characteristic of alight attenuator of the present invention. In the FIG. 2, incorrespondence with the various change of the distance L betweennonlinear optical material 1 and aperture section 2, the relationbetween the light strength of input light and the light strength ofoutput light is being shown. For example, such nonlinear opticalmaterial 1, whose refractive index n₀=1.5, quadratic nonlinearrefractive index n₂=1.8*10⁻⁸ cm²/watt, thickness t=20 mm, and suchaperture section 2 having an aperture whose diameter Ø=10 μm, can beused. In this case, the space area filled with matching oil for keepingthe optical consistency. Here, the used nonlinear optical material ismake up of an Alkali-silicate glass with copper corpuscle dispersion.

[0068] In FIG. 2, it is shown that, when L=12.5 mm, the light strengthof output light is constant approximately no depending upon the lightstrength of input light. Like this way, it is possible to obtain thelight attenuator with constant outputted light strength, no dependingupon the light strength of input light, by using a light attenuatingmethod, which sets most appropriately these parameters of the quadraticnonlinear refractive index n2, the thickness t of the nonlinear opticalmaterial, the distance L between nonlinear optical material 1 andaperture section 2, and the diameter Ø of the aperture of the aperturesection 2.

[0069] Embodiment 2:

[0070]FIG. 3 is a longitudinal section showing the relation between alight attenuator of the present invention in other embodiment and theend portion of an optical fiber.

[0071] In this embodiment, the nonlinear optical material 11 has anincident surface which receives the input light outputted from thereceiving optical fiber 3, and a radiant surface which the light goesout of, as shown by FIG. 3. The incident surface lies at right angles tothe optical axis. And the radiant surface inclines toward the opticalaxis, according to a predetermined angle θ with respect to the verticalplane of the optical axis. The predetermined angle θ is in the range of0°˜90°. The light to be outputted from the inside of the nonlinearoptical material 11 toward the aperture section 2, is refracted on thesloping radiant surface, according to the refractive index of thenonlinear optical material 11.

[0072] When the predetermined angle θ is 0°, the optical beam outputtedfrom the inside of the nonlinear optical material 11 to outside, aresymmetric with respect to the optical axis as a symmetric axis.

[0073] Therefore, when the predetermined angle θ is bigger than 0°, theoptical beam outputted from the sloping radiant surface with the slopingangle θ of the nonlinear optical material 11, are non-symmetric withrespect to the optical axis as shown by FIG. 3(a).

[0074] With the above, the constant output light attenuator, which has acharacteristic different from the embodiment 1 shown by FIG. 1, can beobtained.

[0075] Further, in the FIG. 3(a), the example that the light strength ofinput light is strong is being shown. However, when the light strengthof input light is stronger than that in the example shown by FIG. 1(b),because the optical beam outputted from the inside of the nonlinearoptical material 11 to the outside is strongly refracted, the percentageof the partial light cut off by the aperture section 2 becomes bigger.Therefore, for making the more partial light to certainly enter theaperture of the aperture section 2, it is necessary to set appropriatelythe sloping angle θ.

[0076] That is, in this embodiment, by setting most appropriately theseparameters of the quadratic nonlinear refractive index n2; the thicknesst of the nonlinear optical material; the angle θ of the radiant surfaceof the nonlinear optical material 11; the distance L between nonlinearoptical material 1 and aperture section 2; and the diameter Ø of theaperture of the aperture section 2, it is possible to obtain the lightattenuator with constant outputted light strength, no depending upon thelight strength of input light.

[0077] Embodiment 3:

[0078]FIG. 4 is a longitudinal section showing the relation between alight attenuator of the present invention in more other embodiment andthe end portion of an optical fiber.

[0079] In this embodiment shown by FIG. 4(a), the nonlinear opticalmaterial 11 as shown in FIG. 3 is used. Moreover, on the optical axisbetween the receiving optical fiber 3 and the nonlinear optical material11, a convex lens 5 is placed. The refractive index and the thicknessand others of the convex lens 5 are determined for making the opticalbeam to be gathered at the intersection point of the optical axis andthe sloping radiant surface with a angle θ of the nonlinear opticalmaterial 11. Thus, the input light toward the radiant surface of thenonlinear optical material 11 is focused. In this case, when the valueof the item “|E|²” becomes bigger, the attenuating amount of the inputlight also becomes big.

[0080] Next, to explain the FIG. 4(b), in which a slit section isplaced.

[0081] The slit section 6 has a slit making light to pass through. Theslit is showing a rectangle. The central part c (shown by a Dashed linein FIG. 4(c)) of the slit on the major axis is placed a locationdeviating from the optical axis shown by a DashDot line.

[0082] Thus, the strength distribution of the input light, after passingthrough the slit section 6, changes from normal distribution tonon-symmetric distribution with respect to the optical axis, due toeither a part of the input light at upper edge or a part of the inputlight at under edge is cut off. The input light with the non-symmetricdistribution enters the nonlinear optical material 11 and is stronglyrefracted, then passes through the aperture section 2.

[0083] In this case, as shown in FIG. 4(b), in the upper part of theinput light, the partial light at upper edge is cut off, so that thelight of the upper part, after passes through the slit section 6, entersthe aperture section 2. However, in the under part of the input light,because its partial light at under edge is not cut off, the light of theunder part, after passes through the slit section 6, is cut off by theaperture section 2. Therefore, when the strength distribution indicatesa non-symmetric state by the slit section 6, the remarkable effect oflight attenuating can be obtained in comparison with other case no slitsection.

[0084] In this embodiment, the combination of the nonlinear opticalmaterial 1, the convex lens 5 and the slit section 6 is not limited.

[0085] Embodiment 4:

[0086] In FIG. 5, the embodiment is shown, in which, the nonlinearoptical material 1, the convex lens 5 and the slit section 6 arecombined and placed. However, the nonlinear optical material 11 may beformed like the shape in FIG. 1. The convex lens 5 and the slit section6, respectively, may be individually placed. Also, the convex lens 5 andthe slit section 6 may be combined like this embodiment. In a word, itis fine to select one combination of the nonlinear optical material 1,the convex lens 5 or the slit section 6, if only the combination isoptimized.

[0087] Embodiment 5:

[0088]FIG. 6 shows an example, in which, an optical fiber is used as anonlinear optical material.

[0089] In FIG. 6, the optical fiber 12 is made up of a glass ofmulti-component series. The core portion at center of the optical fiber12 has higher refractive index. In the core portion, corpuscle (cluster)of such as copper or copper chloride or the like is dispersed.Therefore, the core portion is having. In this embodiment, the lightoutputted from receiving optical fiber 3 inputs the optical fiber 12 viathe matching oil. Because the core portion of the optical fiber 12, asstated above, is made up of a corpuscle dispersion glass and has anonlinear optical effect, the refractive index of the core portionchanges depending upon the light strength of the input light.

[0090] The optical fiber 12 serving as nonlinear optical material usedin this embodiment, has the quadratic nonlinear refractive index n2 inabove expression (1). The n2 because has a dependence characteristicdepending upon wavelength, becomes positive by any wavelength.Therefore, when the n2 is positive, in fact, the optical fiber 12performs a function of convex lens. In this case, the light outputtedfrom the optical fiber 12 is refracted and condensed at the focus on theoptical axis of the optical fiber 12. Further, making the focus serve asstarting point, the light spreads symmetrically with respect to theoptical axis. Then a part of the spreading light passes through theaperture of the aperture section 2 placed at the same optical axis.

[0091] As stated above, the aperture section 2 allows only, in thespreading light, the partial light within the radius of the aperture, ormore correctly, the partial light capable of going into the aperture, topass through. Therefore, If only setting most appropriately the radiusof the aperture of the aperture section 2 together with theabove-described parameters, the light outputted from the aperturesection 2, because does not depend upon the light strength of the inputlight inputting the aperture section 2, would become the wishful lightwith constant output strength, then enter the sending optical fiber 4.

[0092] Thus, when a light enters and passes through the nonlinearoptical material, the light is attenuated by refraction at the incidentsurface and the radiant surface of the nonlinear optical material, orthe like. Further, a wishful part of the attenuated light outputted fromthe nonlinear optical material goes into and passes through the apertureof the aperture section. Therefore, the light strength of the outputlight outputted from the aperture section 2 does not change even if thestrength of the input light, that is, the attenuating light inputtingthe aperture section 2 changes. As a result, it is possible to obtain alight attenuator with constant output light.

[0093] In this embodiment, when optical fiber is used as nonlinearoptical material, the length of the optical fiber may be selected morefreely. Further, comparing the optical fiber with an element like Prism,the optical fiber can long get the nonlinear interaction length.Therefore, it is possible to substantially obtain the better nonlinearoptical effect.

[0094] Regarding the nonlinear optical material shown in FIG. 1 or FIG.3, it is necessary to polish its incident and radiant surfaces. However,when the nonlinear optical material is made up of an optical fiber, thepolish processing is not necessary. In this case, there is advantagecapable of simplifying the manufacture process of the nonlinear opticalmaterial.

[0095] Embodiment 6:

[0096]FIG. 7 is showing an example. In which, an optical fiber 13 havinga core portion is used. And the core portion is formed by nonlinearoptical material.

[0097] In this embodiment, the core portion of the optical fiber 13 ismade up of a nonlinear optical material whose quadratic nonlinearrefractive index n2 shown in the above expression (1), is negative withrespect to any wavelength.

[0098] Regarding the optical fiber 13, because the core portion has anonlinear optical characteristic and the negative refractive index n2,when light strength becomes stronger, the difference A of refractiveindex between the core portion and a clod portion would becomes smaller.Thus, because the light confined in the core portion trickles into theclod portion, the attenuating amount of a transmitting light becomesmore.

[0099] Then, the one part of the light outputted from the optical fiber13, is cut off by the aperture section 2 placed at the optical axis, andthe other part of the light enters the aperture of the aperture section2. Therefore, it is possible to obtain the output light with constantlight strength.

What is claimed is:
 1. A constant output light attenuator, comprising: anonlinear optical material receiving an input light, whose refractiveindex changes depending upon the light strength of said input light; andan aperture section which is placed at the optical axis of saidnonlinear optical material for receiving the light outputted from saidnonlinear optical material, and in the receiving light, allow only thepartial light within a definite radius from said optical axis as acenter to pass through.
 2. The constant output light attenuatoraccording to claim 1, wherein said nonlinear optical material is made upof any one of a corpuscle dispersion glass, an optical ceramics and anorganic macromolecule material.
 3. The constant output light attenuatoraccording to claim 1, wherein said nonlinear optical material has anincident surface and a radiant surface, said incident surface lies atright angles to the optical axis, and said radiant surface inclinestoward the optical axis with a predetermined angle.
 4. The constantoutput light attenuator according to claim 1, more comprising: a convexlens, wherein said convex lens is placed at said optical axis, on theincident side of said nonlinear optical material.
 5. The constant outputlight attenuator according to claim 1, more comprising: a slit section,wherein said slit section is set as placing its central part of themajor axis to locate at position deviating from said optical axis, onthe incident side of said nonlinear optical material.
 6. The constantoutput light attenuator according to claim 1, more comprising: a convexlens and a slit section, wherein, said convex lens is placed at saidoptical axis on the incident side of said nonlinear optical material,said slit section is placed between said nonlinear optical material andsaid convex lens by making its central part of the major axis locate aposition deviating from the optical axis.
 7. The constant output lightattenuator according to claim 1, wherein said nonlinear optical materialis made up of an optical fiber whose core has nonlinear optical effect.8. The constant output light attenuator according to claim 7, whereinsaid core is made up of a corpuscle dispersion glass.
 9. The constantoutput light attenuator according to claim 7, wherein said core is madeup of a material that has a quadratic nonlinear refractive indexdepending upon wavelength.
 10. The constant output light attenuatoraccording to claim 9, wherein said core is made up of a material whosequadratic nonlinear refractive index is positive.
 11. The constantoutput light attenuator according to claim 9, wherein said core is madeup of a material whose quadratic nonlinear refractive index is negative.12. A constant output light attenuating method, comprising: receiving ainput light by using a nonlinear optical material whose refractive indexchanges depending upon the light strength of said input light,outputting a light from said nonlinear optical material by making saidinput light pass through said nonlinear optical material; receiving thelight outputted from said nonlinear optical material by using a aperturesection which is placed at the optical axis of said nonlinear opticalmaterial; attenuating the received light by allowing only the partiallight within a definite radius from said optical axis as a center topass through, by said aperture section.
 13. The constant output lightattenuating method according to claim 12, wherein said nonlinear opticalmaterial is made up of any one of a corpuscle dispersion glass, anoptical ceramics and a organic macromolecule material.
 14. The constantoutput light attenuating method according to claim 12, wherein saidnonlinear optical material has an incident surface and a radiantsurface, said incident surface lies at right angles to the optical axis,and said radiant surface inclines toward the optical axis with apredetermined angle.
 15. The constant output light attenuating methodaccording to claim 12, more comprising: placing a convex lens at saidoptical axis of incident side of said nonlinear optical material; andgetting said input light by making a light pass through said convex lensand input said nonlinear optical material.
 16. The constant output lightattenuating method according to claim 12, more comprising: setting aslit section on the incident side of said nonlinear optical material asplacing its central part of the major axis to locate a positiondeviating from the optical axis; and getting said input light by makinga light pass through said slit section and attain to said nonlinearoptical material.
 17. The constant output light attenuating methodaccording to claim 12, more comprising: placing a convex lens at saidoptical axis on the incident side of said nonlinear optical material;placing a slit section between said nonlinear optical material and saidconvex lens as making its central part of the major axis locate aposition deviating from the optical axis; getting said input light bymaking a light after pass through said convex lens, more pass said slitsection and attain to said nonlinear optical material.
 18. The constantoutput light attenuating method according to claim 12, wherein saidnonlinear optical material is made up of an optical fiber whose core hasnonlinear optical effect.
 19. The constant output light attenuatingmethod according to claim 18, wherein said core is made up of acorpuscle dispersion glass.
 20. The constant output light attenuatingmethod according to claim 18, wherein said core is made up of a materialthat has a quadratic nonlinear refractive index depending uponwavelength.
 21. The constant output light attenuating method accordingto claim 20, wherein said core is made up of a material whose quadraticnonlinear refractive index is positive.
 22. The constant output lightattenuating method according to claim 20, wherein said core is made upof a material whose quadratic nonlinear refractive index is negative.